Mazda BT 50 | Camshaft code on Mazda

This is a story about the power of using a scope and how I went about to diagnose a problem on a 2006 Mazda BT 50 Diesel. I was asked to have a look at this car that had a camshaft code P0340. Now, this car had three camshaft sensors replaced (two aftermarket sensors and one original sensor), but the ECM light would come on about once a week with the same code.

I had to see why the ECM was coming up with this code. I set up the PicoScope and connected to the camshaft sensor output and the power and ground, and ran the car to see what was going on with it. At first, everything seemed OK. Then I grabbed the wiring harness and performed a wiggle test to see if I could find any loose connections, and at first, it looked OK. After a bit more wiggling on the wiring harness, however, I had a big smile on my face!

I had enough evidence showing that the ground to the sensor was bad (see screenshots). I then opened up the harness and, knowing it was the ground wire to the sensor (yellow wire), I pulled on it and it just broke apart. I repaired the harness and the car was fixed. This problem would have been very hard to fix without using the PicoScope and, of course, knowing how to set up the scope.